This invention relates to the magnetic control and confinement of diamagnetic fluids such as plasmas and ionized gases. One of the problems in the study and application of plasmas is the confinement and control of the plasma within some region of space. The plasmas of interest for thermonuclear reactions are typically of low density and high temperature. For example, the density may be of the order of 10.sup.15 particles per cubic centimeter, or about 1/25,000 of the normal atmospheric density, and the temperature may be of the order of 10.sup.6 to 10.sup.9 degrees Kelvin. In an earthly environment, it is generally necessary to confine a plasma within a gas tight chamber because of the desired low density and to prevent contamination of the plasma. The high temperatures and generally high thermal conductivity of a plasma make it necessary to substantially eliminate contact between the plasma and the walls of the chamber and/or other solid structures.
Since plasmas are in general diamagnetic, one of the major techniques for plasma confinement has been the enclosure of the plasma within a magnetic field. However, conventional magnetic field confinement systems suffer from various forms of instabilities and/or may give a leaky or imperfect confinement. Descriptions of the properties of plasmas and various conventional methods for their confinement may be found in the published literature. For example, reference is made to the book Controlled Thermonuclear Reactions by Samuel Glasstone and Ralph Lovberg, published by D. van Nostrand Co., Inc., Princeton, New Jersey, 1960, which was prepared under the auspices of the Office of Technical Information, U.S. Atomic Energy Commission. A general description of certain thermonuclear processes which may be applicable to a controlled nuclear fusion reactor is given in U.S. Pat. No. 3,016,342, issued Jan. 9, 1962 to M. Kruskal et al, for a Controlled Nuclear Fusion Reactor.
Two of the major conventional types of plasma confinement systems are the magnetic mirror or pyrotron type systems and the ring type systems. Both the magnetic mirror and ring type systems will be used as examples of embodiments of the subject invention. In a typical magnetic mirror type system, the confinement space is generally in the shape of a right circular cylinder whose length is substantially longer than its diameter. The major confining magnetic field is generally parallel to the axis of the cylinder, and its intensity is greater at the ends of the cylinder than at the middle. The magnetic field generally retards motions of the plasma particles in directions transverse to the field. The stronger magnetic fields at the ends of the confinement region tend to reflect plasma particles back to the central portion of the cylinder. Hence, the name magnetic mirror type system. Two of the major types of plasma leakage of a magnetic mirror type system are leakage out through the ends because of imperfect mirroring, and general diffusion across the magnetic field throughout the confinement region. Other means such as radio frequency fields are sometimes used to further reduce the leakage from the ends. The subject invention is directed to the control of the general leakage across the magnetic field.
Descriptions of magnetic mirror type plasma confinement systems may be found, for example, in U.S. Pat. Nos. 3,003,080, Oct. 3, 1961, R. F. Post, Apparatus for Minimizing Energy Losses from Magnetically Confined Volumes of Hot Plasma; 3,015,748, Jan. 2, 1962, E. C. Hartwig et al, Pyrotron with Translational Closure Fields; 3,093,569, June 11, 1963, R. F. Post, Travelling Wave Pyrotron; 3,101,310, Aug. 20, 1963, R. F. Post, Magnetic End Closures for Plasma Confining and Heating Devices; 3,120,476, Feb. 4, 1964, R. F. Post, Pyrotron Process and Apparatus Utilizing Enhancement Principle; 3,160,566, Dec. 8, 1964, R. A. Dandl et al, Plasma Generator; 3,170,841, Feb. 23, 1965, R. F. Post, Pyrotron Thermonuclear Reactor and Process; 3,257,284, June 21, 1966, R. F. Post, Method of Controlling Plasma Stability; 3,655,508, Apr. 11, 1972, R. L. Hirsch, Electrostatic Field Apparatus for Reducing Leakage of Plasma from Magnetic Type Fusion Reactors; and 3,668,068, June 6, 1972, C. J. H. Watson, Plasma Confinement Apparatus.
In a typical ring type system, the confinement space is generally in the shape of torus. An object is to eliminate the end leakage, such as in magnetic mirror type systems, by closing the confinement space and the major confining magnetic field upon itself so that there are no open ends. A difficulty with ring type systems is that the confining space and confining fields are curved, and the variation of the magnetic field intensity with position is more complex. This can cause additional forms of instability and leakage.
Descriptions of ring type plasma confinement systems may be found, for example, in U.S. Pat. Nos. 2,910,414, Oct. 27, 1959, L. Spitzer, Jr., High Temperature Apparatus; 3,002,912, Oct. 3, 1961, L. Spitzer, Jr., Reactors; 3,012,955, Dec. 12, 1961; R. M. Kulsrud et al, High Temperature Reactor; 3,015,618, Jan. 2, 1962, T. H. Stix, Apparatus for Heating a Plasma; 3,016,341, Jan. 9, 1962, L. Spitzer, Jr., Reactor; 3,029,199, Apr. 10, 1962, W. R. Baker et al, Plasma Device; 3,085,173, Apr. 9, 1963, G. Gibson et al, Apparatus for Trapping Energetic Charged Particles and Confining the Resulting Plasma; 3,088,894, May 7, 1963, H. R. Koenig, Confinement of High Temperature Plasma; 3,143,477, Aug. 4, 1964, Jean-Michel Dolique, Plasma Confining Device; 3,171,788, Mar. 2, 1965, J. G. Gorman et al, Rotating Plasma Device; 3,219,534, Nov. 23, 1965, H. P. Furth, Plasma Confinement Apparatus Employing a Helical Magnetic Field Configuration; 3,278,384, Oct. 11, 1966, A. Lenard et al, Negative V Stellarator; 3,508,104, Apr. 21, 1970, C. M. Braams, Apparatus for the Stable Confinement of a Plasma; 3,607,627, Sept. 21, 1971, H. P. Furth, Stellarator Configuration Utilizing Internal Separatrices; 3,663,362, May 16, 1972, T. H. Stix, Controlled Fusion Reactor; and 3,674,634, July 4, 1972, C. J. H. Watson, Plasma Confinement Apparatus.
Since a plasma is a diamagnetic fluid, it will tend to diffuse or move away from a region of higher magnetic field intensity towards a region of lower magnetic field intensity. In either a magnetic mirror or ring type system, it would be desirable if it were possible to arrange the confining magnetic field so that its intensity always increased with distance away from the central part of the confinement region. Such a field configuration does not appear to be physically possible, at least not for fields which are generally parallel to the central part of an extended confinement region. It is known that the confining field configuration of a ring type system may be arranged so that there are local strong confinement regions in which the magnetic field intensity increases with distance away from the central part of the confinement region. Such systems are sometimes referred to as "bumpy torus" configurations. Descriptions of bumpy torus systems are given in previously referenced U.S. Pat. Nos. 3,085,173 and 3,143,477. Bumpy torus systems generally provide a more effective confinement of the plasma in the local strong confinement regions, but do not provide effective plasma confinement in the regions between the local strong confinement regions.